Flexibility involves movement range in a joint and muscle length. It can be increased by active or passive stretching. Loss of flexibility is a predisposing factor for balance disorders, bad posture, pain and injuries. I recommend at least 30% of your workout routine to be time spent stretching! A short and tight muscle is weak. Logically, when a muscle is weak the solution is to strengthening it, right? The answer is yes. But are your muscles weak because they are atrophied or because they are too tight? A staggering majority of the patients I have treated for the past 21 years are from the second group; the tight ones!